97 F150 won't crank

Wiring, DIY, lighting, etc.
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kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

97 F150 won't crank

Post by kevm14 »

Bill's father in law has one in his backyard that he'd like to resurrect for plow duty. It won't crank. Yes, Ford circled the problem.

BBB Industries has provided this handy starting system wiring diagram.

The truck is an auto. But need to confirm if it has RAP or not. RAP is not Retained Accessory Power. It is anti-theft (my bad but I blame Ford - Remote Anti-theft Personality module is the dumbest and least logical name ever). If it has anti-theft, there is an anti-theft module that controls a starter disable relay. Stupidly (or maybe smartly if they counted on the system failing down the road) the way it works is the starter disable relay is normally closed which enables the starter circuit. If the anti-theft system wants to disable the starter, it actively grounds this relay, which then disables the starter circuit. That's dumb but means the failure mode is that the truck will start which is good depending on when in the truck's life you are dealing with starting issues...

But anyway this is pretty simple. Other than the starter disable/anti-theft relay which is normally closed (and can be jumpered out anyway if suspected), I'd do the following things:
- First I might start at the end, and if the starter solenoid control relay was accessible I would consider jumping that out and seeing if the starter engages. If so, then I'd start at the beginning to see why the ignition switch won't do anything.
- Check fuse 21. Can use test light to check the pin 29 side (downstream side) of the fuse when holding key in crank to see if it lights. If so, this means the ignition switch works and fuse is conducting power.
- With anti-theft, the relay defaults closed but could remove and jump pins 30 and 87A while ignition switch is in crank.
- If still no joy consider checking clutch pedal position switch jumper. It has a simple function but just remove if easy and use DVM to ensure it is shorted in pins 5-6, 1-2 and 3-4. Probably is fine.
- Next, need to examine the range selection switch. I think this is likely the issue. Either remove and jump pins or attempt adjustment. Or try starting in a gear other than P or N if maladjustment is suspected (be careful). If built before 6-24-96, jump pins 4 and 1 together. If it has the newer digital switch (whatever that means) jump pins 10 and 12 while cranking. I suspect this will work as there is nothing else to check if you already did step 1 and the starter engaged.
- Well technically the relay you bypassed in the first step could be the culprit IF the range selector switch passes all the tests.

Then see if she'll actually fire up and run. And move....etc.
Attachments
Ford F150 starter circuitry.pdf
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bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: 97 F150 won't crank

Post by bill25 »

Update.

So, I used the pdf, but didn't read this prior to getting to work as I wanted to see how far off we were.

I think you will notice it is pretty similar.

I started backwards. The owner's manual was missing, so I had no labels or locations based on just the pdf.

We located the starter solenoid (starter motor relay in diagram). I pulled the 12V cable, which broke because the metal in the boot was rusted on to the pin... and we tested it for 12V during ignition crank position. Nothing.

My next step was to test the if the Starter Interrupt relay was not sending a voltage to the starter motor relay, so once it was located on top of the dash under a panel above the passenger airbag, I checked the pinout, and jumpered pins 30 and 87a. Still no voltage at the starter motor relay 12V. Next I tested the Starter interrupt relay, and when applying 12V to pins 30, 85 and 86, I got voltage at 87a, so pretty sure the relay tested good. Next, and I should have done this before messing with the Starter Interrupt Relay I should have tested to see if pin 30 had 12V when ignition in cranking position. I tested, and it didn't. so moving up the chain, I located the fuse in the junction box fuse relay panel. It is fuse 21, 15A. Blown. So need to replace this and retest the Stater Interrupt Voltage, and if good, test the 12V to the starter motor relay.

Also jumped the starter motor relay from the battery directly to the 12V pin using small wire as the repair manual suggests. Nothing. Jumped from the positive battery to the side of the motor relay going directly to the starter, with jumper cable, and it cranked. So, starter is good, starter motor relay also bad.


So far, definitly needs starter motor relay, and 15A fuse. Still need to test the middle if it doesn't just work after replacing those.
Last edited by bill25 on Sun Jan 27, 2019 6:19 pm, edited 1 time in total.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: 97 F150 won't crank

Post by bill25 »

Also forgot to mention that the truck has an aftermarket remote start which also probably has anti-theft stuff too. For added complication.
kevm14
Posts: 15200
Joined: Wed Oct 23, 2013 10:28 pm

Re: 97 F150 won't crank

Post by kevm14 »

bill25 wrote:The owner's manual was missing, so I had no labels or locations based on just the pdf.
Yeah. It could be a good idea to print the diagram and write in the actual location of each item so you don't get confused while checking circuits and components.
bill25 wrote:We located the starter solenoid (starter motor relay in diagram). I pulled the 12V cable, which broke because the metal in the boot was
rusted on to the pin... and we tested it for 12V during ignition crank position. Nothing.
I am not sure the starter solenoid is the same as the starter motor relay in the diagram. The actual starter solenoid should be built into the starter, which is what the diagram shows - it switches high current for the motor itself. Then the starter motor relay is external to the starter and controls the solenoid, which is low current. At least that's how I read the diagram. The box called "starter motor" already has a solenoid depicted in it.

https://www.rockauto.com/en/moreinfo.ph ... 77&jsn=500

The gold canister on top of the motor is the starter solenoid. Ford used to run external solenoids (and external alternator voltage regulators!) which also makes things confusing depending on what you are used to. Virtually every starter in existence looks about like that though.

EDIT: Eh, looks like they still were doing fender mounted starter "solenoids" in 97! That really messes up the terminology but in any event, yes, those do fail and it may in fact need one of those ($20). We are talking about this, right?

https://www.rockauto.com/en/moreinfo.ph ... 77&jsn=653
https://www.rockauto.com/en/moreinfo.ph ... 77&jsn=654

I don't fully understand why they were using that to drive the actual starter solenoid as it looks like it is setup for high current based on the size of the terminals. Because Ford? Shit on my old school GM stuff, the ignition switch crank signal goes through the part/neutral switch but otherwise directly down to the starter solenoid on the starter. No other nonsense in the way.

Anyway make sure the ground isn't the issue as it seems to ground through the body of the unit. One thing you can do is bridge the two large terminals with a screwdriver or something and see if it cranks. But could remove and make sure it has a good ground before replacing.
My next step was to test the if the Starter Interrupt relay was not sending a voltage to the starter motor relay, so once it was located on top of the dash under a panel above the passenger airbag, I checked the pinout, and jumpered pins 30 and 87a. Still no voltage at the starter motor relay 12V. Next I tested the Starter interrupt relay, and when applying 12V to pins 30, 85 and 86, I got voltage at 87a, so pretty sure the relay tested good. Next, and I should have done this before messing with the Starter Interrupt Relay I should have tested to see if pin 30 had 12V when ignition in cranking position. I tested, and it didn't. so moving up the chain, I located the fuse in the junction box fuse relay panel. It is fuse 21, 15A. Blown. So need to replace this and retest the Stater Interrupt Voltage, and if good, test the 12V to the starter motor relay.
This is where I got a little confused. The starter interrupt relay is the first thing in the chain after the fuse. To test that relay, all you need to do is a resistance check across pins 30 and 87A, since it is normally closed to that position. You don't need to apply 12V.
Also jumped the starter motor relay from the battery directly to the 12V pin using small wire as the repair manual suggests. Nothing. Jumped from the positive battery to the side of the motor relay going directly to the starter, with jumper cable, and it cranked. So, starter is good, starter motor relay also bad.
Which pin on the relay? The coil side (to energize the relay and let it pass 12V to the starter solenoid) or the 12V output side (to energize the starter solenoid directly, which tests the path to the solenoid but should be functionally the same as a jumper cable directly to the solenoid)?
So far, definitly needs starter motor relay, and 15A fuse. Still need to test the middle if it doesn't just work after replacing those.
I'm not convinced it needs anything but a fuse. I mean it probably does. But you would need to confirm the connections to/from the starter relay before calling the relay. Also you might be able to borrow another relay temporarily from another system just to avoid buying parts you may or may not need.

Given that the transmission range selection switch went untested, I am still thinking that is an issue here. On the other hand, if the starter motor relay coil malfunctioned and caused a dead short, it would blow fuse 21...linking those two things.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: 97 F150 won't crank

Post by bill25 »

Truck started! So, needed a fuse and there was something up with the starter solenoid/relay, whatever it is. The book said to test by putting 12V to the center post (to replicate the "signal" from the starter), closing the circuit allowing the current from the battery to the starter. This failed. Either the solenoid was bad, or it had a bad ground/contacts. This was replaced, and frankly, was looking pretty bad/rusty etc. so probably good to have swapped out for like 13 bucks anyway.

Replacing the fuse and starter solenoid enabled the truck to successfully start. Hopefully this is good going forward.
bill25
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Joined: Thu Oct 31, 2013 2:20 pm

Re: 97 F150 won't crank

Post by bill25 »

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